1. Field of the Invention
The invention concerns charge transfer devices. It can be applied especially, but not exclusively to devices for the reading of charges generated in photosensitive matrices, notably when these charges have to be transferred directly from an output column of the matrix to a charge transfer shift register.
2. Description of the Prior Art
It has been observed, in certain cases, that it could be useful to have a charge duplication circuit available,
capable of generating and storing, in an ancillary storage zone, an electrical charge which is the exact replica, on a scale of 1 or with a fixed multiplier coefficient which is smaller or greater than 1, of another charge.
To give an example of usefulness such as this, we might indicate the following case. It is sought to transfer a packet of data coming from one output column of a photosensitive matrice to a charge transfer shift register. But it is desired, beforehand, to perform a signal processing operation wherein the considered packet of charges is transferred N times successively from the column to an intermediate storage zone, and the sum of the charges transferred in these N operations is stored in one place. To perform the transfer N times in succession, after each transfer, the transferred charge should be reinjected into the column. The need to be able to both accumulate the charge transferred with the charges coming from the other transfers and reinject this charge into the column led to the making of a charge duplicator which enables both the reinjection of the initial charge and copying it to transfer the copy to wherever the charges which are to be added have accumulated.
As an indication, this signal processing operation was designed to reduce the noise of charge transfer from the column to the charge transfer register, for the noise generated during a transfer is random. If N transfers of the same charge are made, and if the noise generated during a transfer is not correlated with the noise of the other transfers, it is observed and verified by computation that the mean noise affecting the overall charge transferred (namely the sum or average of the transfer charges) is reduced in a ratio of N.sup.1/2 in proportion to the noise affecting a single transfer.
This is therefore why it has been sought to make a charge duplicator. The charge to be read on the output column of the matrix is transferred N times from the column to an intermediate storage zone, and N times in the reverse direction to return to the column, and before each return it is duplicated. The means of the duplicated charges is taken, and it is this mean that has, attached to it, a transfer noise which is reduced and which may be introduced as an output signal into the shift register.
The interested reader may refer to the French patent application filed on this same date, by the same Applicant as that of the present application and mentioning the same inventor.
An object of the present invention is the making of a charge duplicator which introduces as low a noise as possible so that it is possible to generate and store, in a storage region, a charge which is proportionate, with a totally fixed multiplier coefficient, to a reference charge.